The subject matter described herein relates generally to a system and method for conditioning air in an enclosed structure, and more particularly, to system and method for independently controlling temperature and humidity within the enclosed structure.
Enclosed structures, such as occupied buildings, factories and animal barns, generally include an HVAC system for conditioning ventilated and/or recirculated air in the structure. The HVAC system includes a supply air flow path and a return and/or exhaust air flow path. The supply air flow path receives air, for example outside or ambient air, re-circulated air, or outside or ambient air mixed with re-circulated air, and channels and distributes the air into the enclosed structure. The air is conditioned by the HVAC system to provide a desired temperature and humidity of supply air discharged into the enclosed structure. The exhaust air flow path discharges air back to the environment outside the structure. Without energy recovery, conditioning the supply air typically requires a significant amount of auxiliary energy. This is especially true in environments having extreme outside air conditions that are much different than the required supply air temperature and humidity. Accordingly, energy exchange or recovery systems are typically used to recover energy from the exhaust air flow path. Energy recovered from air in the exhaust flow path is utilized to reduce the energy required to condition the supply air.
A Dedicated Outdoor Air System (DOAS) conditions ambient air to desired supply air conditions through a combination of heating, cooling, dehumidification, and/or humidification elements and components. A typical DOAS may include a vapor compression system or a desiccant-based system. When the ambient air is hot and humid, the vapor compression system typically overcools the supply air in order to dehumidify the air. However, this process is inefficient because the air is usually reheated before it is supplied.
In many environments, there is a need to heat or cool the air, but maintain a desired humidity. Conversely, in some environments, one may desire to vary the humidity but maintain a current temperature. However, typical conditioning systems are not configured to vary temperature (sensible energy) and humidity (latent energy) independently of one another. Therefore, while a temperature level may be changed to a desirable level, the resulting change in humidity (or vice versa) may be undesirable.
For example, if an enclosed space is being cooled to a particular temperature by a system, but then the outdoor air temperature decreases, the amount of energy available to reheat the air may also decrease. Consequently, the air supplied to the enclosed space may be lower than desired. While the humidity level within the room may be suitable, the system may be overcooling the enclosed space.